These are notes from me learning AssemblyScript.

AssemblyScript compiles a TypeScript-like language to WebAssembly.

For example, create a calc.ts file:

// calc.ts
export function len(a: string): i32 {
  return a.length;
}

npm install --save-dev assemblyscript
npx asc calc.ts --outFile calc.wasm --bindings esm

Then, in your ESM code, you can import { len } from './calc.js'

WebAssembly can call browser JavaScript code via Host bindings.

For example, utils.js contains:

export function changeTitle(title) {
  document.title = title;
}

Then, in calc.ts, you can define changeTitle() like below and call it from AssemblyScript:

@external("./utils.js", "changeTitle")
declare function changeTitle(title: string): void;

Note:

• JS functions must have one or more fixed signatures.
• async is not supported.

• In tsconfig.json, add "extends": "assemblyscript/std/assembly.json" to use AssemblyScript types.
• @external is not valid TypeScript. Ignore via // @ts-ignore on the line before. Ref

This uses WebAssembly.instantiateStreaming which fetches, compiles, and instantiates a WASM.

export const { fn1, fn2, ... } = await WebAssembly.instantiateStreaming(fetch("file.wasm")).then((r) => r.instance.exports);

WebAssembly does not natively support the following and AssemblyScript bridges some of these:

• Type conversion. Handled via Host bindings
• Garbage collection. AssemblyScript copies strings into WASM and garbage collects them later via exports.__new(size, width).
• Async operations are not currently supported
• DOM manipulation, Fetch, etc. are not possible.
• Exception handling is not supported.